This application in general relates to an electronic stroke indicator which is incorporated into the cylinder housing of a brake actuator in such a way that it is protected from damage from the other components in the brake actuator.
After routine wear, brake actuators typically begin to require adjustment, and may have an undue amount of stroke. In such a condition it is said the brake is out-of-stroke. The prior art has attempted to give warnings to operators of the vehicle when the brakes need adjustment. The indicators which have been incorporated into production units have typically been visual indicators. Thus, an indicator such as a colored stripe which should typically not be visual unless the brake is out-of-stroke is placed on the piston rod.
An operator would periodically check the brake, and if the colored stripe is visible, the operator would have a signal that the brake requires adjustment. Such indicators, while quite valuable could still be improved. First, an indicator that requires visual identification positioned in the neighborhood of the brake is often exposed to mud or dirt. Thus, the visual indicator may not be readily visible. In addition, the visible indicators are typically positioned at the rear of the vehicle. An operator must periodically leave the vehicle to check the brakes. This requires the operator to perform periodic checks in order to insure that the brake does not become too far out of stroke.
Several electronic stroke indicators have been proposed, although they have not been widely utilized in production brake or brake actuators. Typically, these units are incorporated onto a piston rod and monitor the stroke of the piston or the piston rod. When an undue amount of stroke is sensed, a signal is sent to an operator in the vehicle cab. While these proposed systems do address the deficiencies in visual indicators, there have not been systems proposed which would be practically utilizable. The interior of the brake chamber includes a number of components which move relative to each other. The proposed systems have typically included sensors within the chamber, in a location where they are likely to be damaged by other components. As one example, the sensors in a proposed system are placed in the service brake chamber, in the general location of the spring. There has been no attempt to protect the delicate sensor and associated wires from being contacted by the spring and being damaged. A necessary component of reliance on any electronic stroke indicator is a stroke indicator system which is reliable and operable for a relatively long period of time. The prior art systems which have not adequately protected the sensor and associated wires may not be as reliable as would be desirable.
Other proposed sensors include indicators which are mounted on the piston rod outwardly of the chamber away from the spring. The proposed units which have indicators mounted on the piston rod outwardly of the chamber have not necessarily solidly connected the indicator or the sensor to structure at a fixed location. As an example, in one proposed system, the sensor is mounted on a rod adjacent to the piston rod. An indicator is mounted on the piston rod. When the sensor or indicator units on the piston rod are not at fixed locations, the reliability of any out-of-stroke indication from the sensor is in question. This problem is made more severe since the outside area of the brake chamber is in a hostile environment exposed to dirt, rocks and other debris. Such debris could contact the sensor, damaging the sensor, or misaligning the position of the various members. Again, the environment that the brake is disposed in is hostile, and a sensor placed outside of the brake chamber may not always function properly.
Thus, the prior art systems have been unable to provide a sensor system which is protected from the operative elements of the brake, and which may be relied upon to operate for a relatively long period of time.